1. Field of the Invention
The present invention relates to a photoreceptor, and more particularly to a novel electrophotographic photoreceptor comprising a photosensitive layer containing an azo compound.
2. Description of the Prior Art
As the photoreceptor, inorganic photoreceptors having a photosensitive layer comprised principally of an inorganic photoconductive compound such as selenium, zinc oxide, cadmium sulfide, or the like, have heretofore been used widely. These photoreceptors, however, are not necessarily satisfactory with respect to their speed, thermal stability, moisture resistance, durability, and the like. For example, selenium, when crystallized, becomes deteriorated in the characteristics as the photoreceptor, and has therefore difficulty in the production thereof. The crystallization is sometimes caused by heat or finger prints, resulting in the deterioration of the characteristics of selenium as the photoreceptor. Cadmium sulfide is disadvantageous with respect to the moisture resistance and durability thereof. Zinc oxide also has drawbacks with respect to durability and the like.
In recent years, the research and development of new organic photoreceptors having a photosensitive layer composed principally of various organic photoconductive compounds have been made for the purpose of overcoming such shortcomings of these inorganic photoreceptors. For example, Japanese Patent Examined Publication No. 10496/1975 describes an organic photoreceptor having a photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. This photoreceptor, however, is not necessarily satisfactory in speed and durability. In order to improve such disadvantages, an attempt is made to develop a higher performance organic photoreceptor, whose carrier-generating function and carrier-transport function are allotted to different materials.
Such function-separated-type electrophotographic photoreceptors permit the selection of materials thereof from an extensive range, thus facilitating relatively the production of optional characteristic photoreceptors. For this reason, many studies have been made on photoreceptors of this type.
For the function-separated-type electrophotographic photoreceptor, a number of compounds are proposed as the carrier-generating material. An example of inorganic compounds that can be used as the carrier-generating material is amorphous selenium as described in Japanese Patent Examined Publication No. 16198/1968. This is to be used in combination with an organic photoconductive compound, but does not eliminate the disadvantage that the carrier-generating layer composed of amorphous selenium is crystallized when heated, whereby its characteristics as the photoreceptor is deteriorated.
Many electrophotographic photoreceptors which use organic dyes or pigments as the carrier-generating material also have been proposed. For example, those electrophotographic photoreceptors containing bisazo or trisazo compounds are disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 12742/1979, 74746/1982 and 69148/1980. These bisazo or trisazo compounds, however, do not necessarily provide satisfactory characteristics such as speed, residual electric potential and stability when used repeatedly, and they restrict the carrier-transport material-selectable range, thus satisfying no adequately wide requirements for the electrophotographic process.
Further, in recent years, gas lasers such as the Ar laser, He-Ne laser, etc., and semiconductor lasers have now been used. These lasers are characterized by being ON/OFF turnable in time series, and are particularly promising as the light source for those printers such as intelligent copiers, image-processing function-having copiers, and computer output printers. Of these, the semiconductor laser requires no electric signal/optical signal conversion element such as the acoustooptic element, etc., and can be made compact and lightweight, thus having come to attention. The semiconductor laser, however, produces a lower output than does the gas laser, and has a longer oscillation wavelength (longer than about 780 nm). Accordingly, the semiconductor laser as it is can not be applied to those conventional photoreceptors whose spectral sensitivity is on the much shorter wavelength side than the oscillation wavelength.